The present application claims priority to Japanese Application No. P11-179291 filed Jun. 25, 1999 and Japanese Patent Application P2000-005116 filed Jan. 14, 2000 which applications are incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to a photocatalyst, employing fullerene as a material, a manufacturing method for the photocatalyst, and a gas decomposition method and apparatus employing the photocatalyst.
2. Description of Prior Art
For reducing harmful ingredients in air, such as aldehyde or carbon monoxide, a photocatalyst composed of fullerene as a main material has recently been developed.
That is, evaporated film of fullerene is known to exhibit a catalytic action of decomposing harmful ingredients on light irradiation.
However, this fullerene is not fully satisfactory mainly with respect to durability. Before explaining the reason therefor, it is felt to be necessary to consider the historical background of development of the material fullerene.
Fullerene is a series of carbon compounds composed only of carbon atoms, as is diamond or graphite. The existence of fullerene was confirmed in the eighties. That is, it was found in 1985 in a mass analysis spectrum of a cluster beam by laser ablation of carbon. It was, however, five years later that the manufacturing method in reality was established. Specifically, a manufacturing method for fullerene (C60) by arc discharge of a carbon electrode was first found in 1990. Since then, fullerene is attracting notice as a carbonaceous semiconductor material (see Kratschmer, W., Fostiropoulos, K, Huffman D. R. Chem. Phys. Lett. 1990, 170, 167. Kratschmer, W. Lamb L. D., Fostiropoulod. K, Huffman, D. R. Nature 1990, 347,354).
Fullerene is a spherical carbon Cn (n=60, 709, 76, 78, 80, 82,84, . . . ) which is a molecular aggregate resulting from spherical aggregation of an even number not less than 60 of carbon atoms. Representative of the fullerenes is C60 with 60 carbon atoms as aforesaid and C70 with 70 carbon atoms. Of these, the C60 fullerene is of a polyhedral structure termed frusto-icosahedron obtained on cutting off the apices of the regular icosahedron to yield a regular pentagon. Thus, the C60 fullerene has a molecular structure of what may be termed a soccer ball type in which its 60 apices are all occupied by carbon atoms. On the other hand, C70 has what may be termed a rugby ball type molecular structure.
In a C60 crystal, C60 molecules are arranged in a face-centered cubic structure. It has a band gap of approximately 1.6 eV and may be deemed as a semiconductor. In an intrinsic state, it has an electrical resistance of approximately 1014 xcexa9/cm at 500xc2x0 C. It has a vapor pressure of approximately 1 mm Torr and, on sublimation, it is capable of vapor depositing a thin film. Not only C60 but other forms of the fullerene are readily vaporized in vacuum or under reduced pressure and hence are able to yield an evaporated film easily.
However, the molecules of fullerene forms, such as C60 or C70, the most mass-producible, are of zero dipole moment, such that evaporated films produced therefrom are fragile in strength, because only the Van der Waals force acts between its molecules. Thus, if the evaporated film is exposed to air, molecules of oxygen or water tend to be diffused and intruded into the gap between the fullerene molecules (FIG. 2), as a result of which the evaporated film is not only deteriorated in structure but adverse effects may be occasionally produced in its electronic properties.
This fragility of the fullerene poses a problem that is not negligible mainly in durability when the film is utilized for a photocatalyst discussed above.
It is therefore an object of the present invention to provide a photocatalyst, having superior durability, ascribable to the use of a film belonging to the fullerene series but different from the evaporated film, a manufacturing method for the photocatalyst, and a gas decomposition method and apparatus employing the photocatalyst.
The present invention provides a photocatalyst having a fullerene polymer film.
The present invention also provides a method for producing a photocatalyst including forming the fullerene polymer film by polymerizing fullerene molecules by electron beam polymerization, electromagnetic wave polymerization or electronic polymerization, and getting fine metal particles carried by sputtering, evaporation or coating on the surface of the fullerene polymer film.
The present invention also provides a method for producing a fullerene polymer including evaporating fullerene molecules, and illuminating electromagnetic waves, such as RF plasma, thereon, to polymerize the fullerene molecules, and a manufacturing method for a functional element employing the fullerene polymer film as a functional element constituting layer.
The present invention also provides a gas decomposition apparatus including a light source, and a fullerene polymer film contacted with a gas for decomposition.
The present invention also provides a gas decomposition method including contacting a gas for decomposition with a fullerene polymer film under light illumination.
The fullerene polymer film employed in the present invention is formed from fullerene molecules as a starting material, by e.g., electromagnetic polymerization method, such as plasma polymerization or microwave polymerization, as later explained. The fullerene molecules are polymerized through the state of electronic excitation.
This fullerene polymer film has a film structure in which fullerene molecules are strongly bonded together by covalent bonds, as shown in FIGS. 3 and 4, and is appreciably higher in strength than the fullerene polymer film, while being dense and pliable. If the film is exposed to air, oxygen or water molecules can hardly be intruded into the inside of the film in distinction from the evaporated film. Therefore, the fullerene polymer film is a fullerene based material having superior durability. The evaporated film tends to lose its properties, evaluated in air, in approximately one day, whereas, if the evaporated film is polymerized, its properties are hardly changed even after lapse of one month.
Also, with the fullerene polymer, functional element and the method for producing the fullerene polymer or the functional element, according to the present invention, an evaporated film of fullerene molecules is first formed and polymerized on irradiation of electromagnetic waves. Thus, the thickness of the evaporated film can be measured with a film thickness meter to control the evaporation conditions, such as evaporation temperature, based on the measured information, to form a desired evaporated film at all times. Therefore, the film thickness of the fullerene polymer film by irradiation of electromagnetic waves can be easily and correctly controlled to realize a desired film thickness at all times.
Moreover, since the evaporated fullerene film undergoes polymerization, on irradiation with the electromagnetic waves, as the structure of the fullerene molecules of the evaporated film is maintained, it is possible to realize a fullerene polymer film of a neat structure having the fullerene molecule skeleton. If an organic film is present in the underlying layer, it is not damaged by the evaporated film formed thereon. In addition, due to the presence of the evaporated film, the underlaying layer can also be protected against radiation of the electromagnetic waves.
Similarly to the evaporated fullerene film, the fullerene polymer film is made up of fullerene molecules, so that the fullerene polymer film exhibits the catalytic action by light irradiation.
The effect of light irradiation on the fullerene has been investigated meticulously since the establishment of the manufacturing method in 1990.
Most noteworthy is the fact that, on electronic excitation on light irradiation, the fullerene is first excited from the ground state to the excited single state, after which it can readily undergo inter-state intersection to the electronically excited triplet state. The electronically excited low-energy state of the fullerene may be deemed to be a singlet (xcfx80-xcfx80*) state. In a molecule of planar xcfx80-covalent system, the inter-state intersection between the singlet (xcfx80-xcfx80*) state and the triplet (xcfx80-xcfx80*) state is a ban, whereas, with the fullerene molecules, the "sgr" and xcfx80 trajectories cease to cross each other due to the radii of curvature thereof. Stated differently, the "sgr" and xcfx80 trajectories are mixed together to contribute to inter-state intersection between different spin multiplicities by spin trajectory interaction. Among different fullerene molecules, C60 is known to be high in the inter-state intersection probability.
If the fullerene is contacted with oxygen, the energy is transferred from the fullerene of the excited triplet state to the site of contact. On reception of this energy, oxygen transfers through the ground triplet state to the excited singlet state. This oxygen in an unstable state is termed active oxygen.
Since the photocatalyst of the present invention has a fullerene polymer film, if its surface is contacted with the gas for processing, such as the gas containing harmful ingredients in air, there occurs the above-mentioned catalytic action on the film surface, by the light illumination, thus decomposing the harmful ingredients in the gas for processing. The evaporated film is problematic in that oxygen molecules diffused and invaded into the molecular interstices are activated to produce the phenomenon of oxidation in the inside of the film, that is decomposition of the harmful ingredients, so that the evaporated film is lowered in its catalytic action and hence in durability due to the produced gas ingredients.
In the present invention, such a photocatalyst carrying fine metal particles of, for example, platinum or palladium, on the surface of the fullerene polymer film, is preferred. In such case, the catalytic effect is better than if no metal particles are carried on the catalyst surface.
The film can be deposited on the fullerene polymer film by such techniques as sputtering, evaporation or coating.
The gas decomposition apparatus according to the present invention at least includes a light source and a fullerene polymer film and is able to decompose the gas for processing containing harmful components by having the gas for processing contacted with the fullerene polymer film under light irradiation.
The photocatalyst according to the present invention, employing the fullerene polymer film, is far better in durability than the photocatalyst employing a fullerene polymer film. This effect can be further improved by having fine metal particles carried on the fullerene polymer film by sputtering, evaporation or coating. In the gas decomposition apparatus according to the present invention, having the fullerene polymer film and the light source, the gas for processing is contacted with the fullerene polymer film under light illumination, so that harmful or polluting substances, such as aldehyde or carbon monoxide, can be decomposed effectively.
Also, according to the present invention, in which the evaporated film of the fullerene molecules is first formed and subsequently polymerized on irradiation of the electromagnetic waves, desired evaporated films can be formed by measuring the evaporated film thickness by a film thickness meter and by controlling the evaporation conditions, such as evaporation temperature, and hence the film thickness of the fullerene polymer film by irradiation of the electromagnetic waves can be easily accurately controlled to produce the desired film thickness.
In addition, the evaporated fullerene film undergoes polymerization, on irradiation of the electromagnetic waves, as the structure of the fullerene molecules is maintained, as a result of which a fullerene polymer film of a neat structure may be formed which retains the fullerene molecular skeleton. If an organic acid etc. is present in an underlayer, the underlayer is not damaged by the overlying evaporated film. On the other hand, the underlying layer can be protected from the radiation of the electromagnetic waves by the evaporated film.